A wellbore generally refers to a hole drilled into the earth for the extraction of hydrocarbon-based materials such as, for example, oil and natural gas. Because the term “wellbore” generally includes the open hole or uncased portion of a well, the term “wellbore” typically refers to the space bounded by the wellbore wall—that is, the face of the geological formation that bounds the drilled hole. A wellbore is sometimes referred to as a “borehole.”
A perforation is the communication tunnel created from the casing or liner into the reservoir formation, through which oil or gas is produced. The most common method of perforating uses jet perforating guns equipped with shaped explosive charges. However, other perforating methods include bullet perforating, abrasive jetting or high-pressure fluid jetting. Perforation density is the number of perforations per linear foot. The term perforation density is used to describe the configuration of perforating guns or the placement of perforations, and is often abbreviated to spf (shots per foot). An example would be an 8 spf perforating gun. Perforation penetration is a measure, or indicator, of the length that a usable perforation tunnel extends beyond the casing or liner into the reservoir formation. In most cases, a high penetration is desirable to enable access to that part of the formation that has not been damaged by the drilling or completion processes. Perforation phasing is the radial distribution of successive perforating charges around the gun axis. Perforating gun assemblies are commonly available in 0-, 180-, 120-, 90- and 60-degree phasing. The 0-degree phasing is generally used only in small outside-diameter guns, while 60, 90 and 120 degree phase guns are generally larger but provide more efficient flow characteristics near the wellbore.
A perforating gun is a device used to perforate oil and gas wells in preparation for well production. Such guns typically contain several shaped explosive charges and are available in a range of sizes and configurations. The diameter of the gun used is typically determined by the presence of wellbore restrictions or limitations imposed by the surface equipment. The perforating gun, fitted with shaped charges or bullets, is lowered to the desired depth in a well and fired to create penetrating holes in casing, cement, and formation. Thus, to perforate is to pierce the casing wall and cement of a wellbore to provide holes through which formation fluids may enter or to provide holes in the casing so that materials may be introduced into the annulus between the casing and the wall of the borehole.
Current drilling has focused more on directional drilling. Directional drilling results in the creation of lateral well bores. Lateral well bores create many difficulties including difficulties with respect to perforating. It is appreciated that arcuate and lateral portions of a well bore create specific problems, especially with respect to perforating. Further, the longer the lateral portions of the well bore, the more difficult it is to achieve effective perforations. Thus, as drilling practices are directed more toward directional drilling, and directional drilling creates more and longer lateral well bores, the need for effective perforating techniques is greatly increased. The need for effective perforating techniques has long existed and the need increases proportionately with the increase in directional drilling.
There has been a long felt need to perforate accurately and efficiently. The types of charges available have restricted such perforating. The available charges are a restriction to enhancing the performance of the perforation.
The characteristics of the perforation have been and continue to be inferior. Particularly, the need for a continuous, normal perforation, free from disruption, has long been sought after, but not achieved.
The ability to enhance the performance of the perforation has long eluded the art. Especially, the ability to assist and aid the existing charges in the enhancement of the capacity and forcefulness of the perforation has long been desired.
Conventional perforating guns are lowered, via coiled tubing or a similar conduit within a pre-existing casing string, to a desired depth, actuated to perforate in an outward direction, through the casing and into the formation, then removed to allow for production from the formation. As such, current perforating practices require much equipment and manpower. For example, the use of coiled tubing to initiate the perforating process is costly, time consuming, laden with the need for manpower, and prone to have safety problems.
Alternatives to conventional perforating guns include various casing-conveyed systems, typically attached to or otherwise positioned relative to the exterior of the casing, then actuated to penetrate inward into the casing wall. Current perforating devices adapted for conveyance during casing installation are problematic. Such perforating devices require secondary control lines that extend to the surface, and are tedious to install and use. It is long desired to have a “disappearing” perforating gun that is unobtrusive after it has been used.